Often, to protect pipe, other metal members or metal structures, the outer surface of the object is coated. There are many coatings used for protection, including a variety of epoxies. For example, the outer surface of a steel pipe, when used in an outdoor application, is normally provided with a corrosion resistant coating, such as a fusion bonded epoxy coating. Federal law requires that underground pipelines be provided with a corrosion coating and that the corrosion coating be intact prior to installation. 49 C.F.R. .sctn..sctn.192.451-192.491 (1989). Often there are manufacturing defects in pipe that prevent the corrosion coating from being continuous. These defects, called "slivers," are similar to splinters in wood or burrs in the pipe steel. The "slivers" are large enough that the fusion bonded epoxy corrosion coating does not cover them, resulting in "holidays" or holes in the coating. Moreover, often there are so many "slivers" and resulting "holidays" that the coating cannot be "patched" and the pipe cannot be installed. Efforts to develop a cost effective means for salvaging such pipe have not been successful. For example, it is not cost efficient to remove a fusion bonded epoxy coating, refinish the surface of the pipe to eliminate the "slivers," and then recoat the pipe. Even if the pipe is recoated, the "holidays" often reappear. Thus, there is a need for a cost efficient means to repair fusion bonded epoxy corrosion protection coatings riddled with "holidays" created by "slivers."
In other situations, there is no fusion bonded epoxy coating, and corrosion protection must be applied directly to the metal surface. This is particularly difficult when the metal surface is irregular. Such condition is often referred to as "poor steel."
In addition to corrosion protection, when the pipe is buried in the ground the pipe is often further protected. For instance, at underground road crossings, the pipe is usually enclosed within a tubular metal casing and is supported within the casing by a mechanical device known as a pipeline casing insulator. In addition to supporting the pipe, the pipeline casing insulator prevents damage to the pipe and any pipe coating when the pipe is drawn through the casing during installation, and it electrically insulates the pipe from the casing.
A typical example of a metal pipeline casing insulator is illustrated in Pipeline Casing Insulators, Casing End Seals and Wall Penetration Seals, Section 100, Bulletin No. 14825 12/85, Maloney Pipeline Products Co. of 5200 Cedar Crest, Houston, Tex. 77087. The components of such a pipeline casing insulator, the band, the rubber liner, the runners and the mounting hardware, are provided as separate components that are relatively expensive and that require time consuming field assembly. Additionally, the metallic components of such a pipeline casing insulator can damage the integrity of the corrosion resistant coating during assembly. A pipeline casing insulator utilizing polymer concrete, as described in U.S. Pat. No. 4,928,736, however, requires no field assembly and is less expensive than typical metal pipeline casing insulators. Moreover, it contains no metal parts that could damage the pipe coating during attachment or later interfere with cathodic protection.
Although the polymer concrete pipeline insulator solved problems associated with traditional pipeline casing insulators, the utilization of casings at underground crossings is expensive and time consuming. Thus, it is desirable to install pipelines at underground road crossings without the use of casings. The method of installing pipelines at underground road crossings without casings is commonly referred to as the "slick bore" method. Alternatives for protecting the pipe coating during "slick bore" installation have been tried, but none of these prior alternatives are without problems.
One prior alternative for protecting pipe during "slick bore" installation is to coat the outer surface of the pipe, in addition to any corrosion coating, with portland cement concrete. The portland cement concrete coating is usually a minimum of 1 1/2"-2" in thickness. The diameter of the pipe, therefore, is increased by a minimum of 3"-4". Thus, a larger diameter bore for the underground crossing is required for the portland cement coated pipe than for pipe not coated with portland cement concrete. The increase in the bore diameter increases the cost of installation. Additionally, because of the heavy coating of portland cement concrete, the weight of the pipe is greatly increased. The increase in weight increases the shipping costs of the pipe, if coated prior to shipment to the field, increases the difficulty of installation, and increases the risk of damage to the pipe structure during installation of the pipe. Moreover, the portland cement coating process, including application and setting or preliminary curing, typically requires several days to be completed. It is a time consuming alternative.
Another prior alternative for protecting pipe during "slick bore" installation is to increase the thickness of a corrosion coating, such as a fusion bonded epoxy coating. Even with the increase in thickness of the coating, however, the pipe corrosion coating is usually damaged during installation to the extent that "holidays" in the coating result. Thus, the integrity of the corrosion coating is not maintained.
As with installation at underground crossings, when pipe is buried in a rocky terrain, the pipe and any coating must be protected. Generally, the prior art rocky terrain protection systems are installed mechanically, such as with tape. One such rocky terrain protection system is described in Pipe Protection Materials, Standard Rock Shield, Protective Padding, Rock Shield Tape #400, Pressure Sensitive, PP-79 4-18, Johns-Manville, Ken-Caryl Ranch, Denver, Colo. 80217. Field installation of such prior art rocky terrain protection systems is time consuming and labor intensive. Not all rocky terrain protection systems are installed in the field. One such system is described in Rock Jacket, Shaw Jacket Systems by Shaw Pipe Protection Limited of 25 Bethridge Road, Rexdale, Ontario, Canada M9W 1M7. The Rock Jacket System includes a reinforced wire mesh coating and an outer tape wrap. The Rock Jacket system absorbs water so that it conducts electricity.
Just as is the case when pipe is installed at underground crossings, it is possible to protect pipe in rocky terrain by portland cement concrete coatings. As described above, however, portland cement concrete coatings increase the weight of the pipe and are time-consuming to install.
In situations where pipe is used to conduct heated product such as oil or gas from deep reservoirs through cold environments such as sea water, it is necessary to retain as much heat within the pipe as possible to reduce condensation within the pipe. Accordingly, it is necessary that the pipe coating prevent the loss of heat to the environment in which the pipe is being used.
One object of the present invention is to provide an improved coating that eliminates the need for casing and pipeline casing insulators for installation of pipe at underground crossings, without greatly increasing the weight of the pipe and without increasing the risk of damage to the pipe structure and any subcoating during installation.
Another object of the present invention is to provide an improved coating that protects pipelines and any subcoatings, such as fusion bonded epoxy, during installation of pipelines in rocky terrain. Moreover, it is an object of the present invention to provide an improved coating that so protects the pipelines and any subcoatings without time consuming field installation.
Another object of the present invention is to provide an improved coating that salvages fusion bonded epoxy coated pipe in which "holidays" are formed in the fusion bonded epoxy coating by "slivers" in the pipe.
Still another object of the present invention is to provide an improved coating that protects pipe, other metal members and metal structures from abrasion and corrosion without the need of a corrosion protection subcoating.
A further object of the present invention is to provide an improved coating that insulates pipe, other metal members and metal structures from electrical charges.
Additionally, it is an object of the present invention to provide an improved coating that protects pipe, other metal members, metal structures and any subcoatings in high temperature environments.